In an optical communication system, terminal channel cards are usually located at secure locations, providing sufficient security to prevent tampering and wire tapping. However, as optical amplification and cross-connection are required in optical networks, there are several locations outside the terminal building, where access to the optical signal can be obtained without much effort and without interrupting the optical fiber. Especially, in optical amplifiers a monitor port allows access to the full spectrum of a WDM signal with sufficient power to detect the signal error free. In this case, only a readily available optical filter is required to separate the WDM channel of interest from the other channels of a WDM system.
In some implementations of an R-OADM (reconfigurable optical add-drop multiplexer) node, even output connectors are available that allow access to single channels of a WDM system. While it is desirable to maintain these optical ports available for service personnel to connect measurement equipment (power meter, optical spectrum analyzer) for maintenance tasks, it is undesirable that any of these ports can be used, undetected by the owner or operator of the transmission system, to wiretap the optical signal.